Mems resonator and manufacturing method of the same

ABSTRACT

A method is for manufacturing a microeletromechanical system resonator having a semiconductor device and a microelectromechanical system structure unit formed on a substrate. The method includes: forming a lower electrode of an oxide-nitride-oxide capacitor unit included in the semiconductor device using a first silicon layer; forming, using a second silicon layer, a substructure of the microelectromechanical system structure unit and an upper electrode of the oxide-nitride-oxide capacitor unit included in the semiconductor device; and forming, using a third silicon layer, a superstructure of the microelectromechanical system structure unit and a gate electrode of a complementary metal oxide semiconductor circuit unit included in the semiconductor device.

BACKGROUND

1. Technical Field

The present invention relates to a MEMS resonator and a manufacturingmethod of the same.

2. Related Art

In recent years, microeletromechanical systems (MEMS) have exhibited afavorable growth in the usage thereof for apparatuses such asacceleration sensors and video devices. There are variousinterpretations as to what MEMS include conceptually. While in somecases, it is also referred to as “micro machine”, or “micro systemtechnology (MST)”, MEMS generally mean “fine functional devices producedusing semiconductor manufacturing techniques”. Those devices aremanufactured based on fine processing techniques developed forfabrication of semiconductors. Currently, MEMS are manufacturedindependently from other manufacturing processes, or, produced onto anintegrated circuit (IC) in a process after completing the manufacturingof IC. The field of applications of MEMS includes electric appliancesand automobiles, and the field is still expanding. Processes formanufacturing MEMS have been modified based on common microfabricationtechniques of semiconductors. For example, capacitive pressure sensorsare known, including a diaphragm that is formed on the samesemiconductor substrate concurrently to the formation of a gate of anactive element. Refer to JP-A-2004-526299 as an example. Moreover, it isknown that in order to make a pressure sensor which combines within asemiconductor device smaller, with the higher functionality andreliability, a conductive layer included in an electric circuit is usedfor forming a pressure detection unit included in a pressure sensor.Refer to JP-A-2006-126182 as an example.

In JP-A-2004-526299 however, only a static capacitive MEMS structure anda complementary metal oxide semiconductor (COMS) circuit are formedconcurrently. In JP-A-2006-126182, although a MEMS structure, a COMScircuit, and an oxide-nitride-oxide (ONO) capacitor are formed on asingle chip, the MEMS structure is formed in an interconnection layer,while the lower electrode of the ONO capacitor uses a diffusion layer ofa silicon substrate. That is to say, the three devices (CMOS circuit,ONO capacitor, and MEMS structure) have not yet been formedconcurrently, while two of the three (CMOS circuit and ONO capacitor,or, MEMS structure and CMOS circuit) have been. The above resulted inthe following problems. If the ONO capacitor is not included andtherefore not used, limitations are imposed on the structure (lessvariations) of the CMOS circuits such as analog-digital conversioncircuit, and other circuits requiring capacitor other than substrateelectrode. Moreover, a system in package (SIP) structure in which theONO capacitor is packaged in a separate chip results in problems such asincreased number of processes, increased cost, and noises generated by awire bonding of interconnections. If the MEMS structure is not included,it results in the aforementioned problems such as increased noise.Further, the MEMS are processed incrementally in pre/post process. Thiscauses an increase in the number of processes and costs, since theprocessing steps cannot be carried out concurrently.

An advantage of the invention is to provide a method for manufacturing aMEMS resonator which simplifies processes and reduces the costs, as wellas to provide a MEMS resonator produced with the method.

According to a first aspect of the invention, a method for manufacturinga MEMS resonator includes the following steps. Forming a lower electrodeof an ONO capacitor unit included in the semiconductor device using afirst silicon layer; forming, using a second silicon layer, asubstructure of the MEMS structure unit and an upper electrode of theONO capacitor unit included in the semiconductor device; and forming,using a third silicon layer, a superstructure of the MEMS structure unitand a gate electrode of a CMOS circuit unit included in thesemiconductor device. Here, the MEMS resonator includes a semiconductordevice and a MEMS structure unit that are formed on a substrate.

With the above method, the MEMS structure, the CMOS circuit, and the ONOcapacitor are packaged on a single chip. This not only simplifies theprocess and reduces the cost but also simplifies the system and makesthe system effective against noise.

According to a second aspect of the invention, a MEMS resonator includesa MEMS structure unit formed on the substrate, and a semiconductordevice formed on a substrate, the semiconductor device including an ONOcapacitor unit and a CMOS circuit unit.

With the above method, the MEMS structure, the CMOS circuit, and the ONOcapacitor are packaged on a single chip. This not only simplifies theprocess and reduces the cost, but also simplifies the system and makesthe system effective against noise.

In this case, the MEMS resonator may include: a first silicon layer usedfor forming a lower electrode included in the ONO capacitor unit; asecond silicon layer used for forming a substructure included in theMEMS structure unit and an upper electrode included the ONO capacitorunit; and a third silicon layer used for forming a superstructureincluded in the MEMS structure unit and a gate electrode included in theCMOS circuit unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic plan view illustrating a MEMS resonator accordingto one embodiment to which aspects of the invention are applied.

FIG. 2 is a sectional view illustrating a MEMS resonator according toone embodiment to which aspects of the invention are applied.

FIGS. 3A to 3D are drawings for describing a manufacturing method of theMEMS resonator according to one embodiment to which an aspect of theinvention is applied.

FIGS. 4A to 4D are drawings for describing the manufacturing method ofthe MEMS resonator according to one embodiment to which an aspect of theinvention is applied.

FIGS. 5A and 5B are drawings for describing the manufacturing method ofthe MEMS resonator according to one embodiment to which an aspect of theinvention is applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments in which the invention is applied will now be described withreferences to the accompanying drawings.

FIG. 1 is a schematic plan view illustrating a MEMS resonator accordingto one embodiment to which aspects of the invention are applied. FIG. 2is a sectional view illustrating a MEMS resonator according to oneembodiment to which aspects of the invention are applied. As shown inFIG. 1, the MEMS resonator according to one embodiment of the inventionincludes a substrate 10, a MEMS structure unit 4 formed on the substrate10, and a semiconductor device including an ONO capacitor unit 6 and aCMOS circuit unit 8.

A single-crystal semiconductor substrate may be used as the substrate10, and examples of materials includes silicon (Si) and gallium arsenide(GaAs). A silicon single-crystal substrate is particularly desirable.The thickness of the substrate 10 ranges from 100 to 1000 μm.

As shown in FIG. 2, a device isolation oxide film 12 is formed on thesurface of the substrate 10. The device isolation oxide film 12 is athermal oxidation film. The device isolation oxide film 12 is a fieldinsulating film formed with a local oxidation of silicon (LOCOS) method,and the thickness thereof ranges from 0.1 to 2 μm. The MEMS structureunit 4 and the ONO capacitor unit 6 are arranged on the device isolationoxide film 12.

A base nitride film 14 is formed on the surface of the device isolationoxide film 12. The base nitride film 14 is a SiN film, and the thicknessthereof ranges from 0.1 to 2 μm. The base nitride film 14 is neededunder the MEMS structure unit 4, and may also be under the ONO capacitorunit 6.

A substructure 16 and a superstructure 18, both included in the MEMSstructure unit 4, are formed on the surface of the base nitride film 14in a region of the MEMS structure unit 4. The substructure 16 in theMEMS structure unit 4 is formed using a second silicon layer 52 (referto FIG. 4A). The substructure 16 in the MEMS structure unit 4 and anupper electrode 30 of the ONO capacitor unit 6 are formed simultaneouslyusing the second silicon layer 52. The superstructure 18 in the MEMSstructure unit 4 is formed using a third silicon layer 54 (refer to FIG.4C). The superstructure 18 in the MEMS structure unit 4 and a gateelectrode 34 of the CMOS circuit unit 8 are formed simultaneously usingthe third silicon layer 54. Examples of materials used in thesubstructure 16 of the MEMS structure unit 4 include polycrystallinesilicon (poly-Si) and amorphous silicon. The thickness of thesubstructure 16 of the MEMS structure unit 4 ranges from 0.05 to 100 μm.Examples of materials used in the superstructure 18 of the MEMSstructure unit 4 include polycrystalline silicon (poly-Si) and amorphoussilicon. The thickness of the superstructure 18 of the MEMS structureunit 4 ranges from 0.05 to 100 μm.

A second field interlayer film 22 is formed over the substructure 16 ofthe MEMS structure unit 4, and contact holes 24 are formed over thesubstructures 16 in the MEMS structure unit 4.

A lower electrode 26 of the ONO capacitor unit 6 is formed on thesurface of the base nitride film 14 in a region of the ONO capacitorunit 6. The lower electrode 26 of the ONO capacitor unit 6 is formedusing a first silicon layer 26 (refer to FIG. 3A). Examples of materialsused in the lower electrode 26 of the ONO capacitor unit 6 includePoly-Si and amorphous Si. The thickness of the lower electrode 26 of theONO capacitor unit 6 ranges from 0.05 to 100 μm.

An ONO capacitor interlayer insulating film 28 is formed on the lowerelectrode 26 of the ONO capacitor unit 6. The ONO capacitor interlayerinsulating film 28 is formed including therein three layers; a lowerinterlayer insulating film 28A, an intermediate interlayer insulatingfilm 28B, and an upper interlayer insulating film 28C (refer to FIG.3D). Materials used for the ONO capacitor interlayer insulating film 28are SiO₂, Si₃N₄, and SiO₂ for the lower interlayer insulating film 28A.the intermediate interlayer insulating film 28B, and the upperinterlayer insulating film 28C respectively. The thickness of all theabove three layers constituting the ONO capacitor interlayer insulatingfilm 28 ranges from 1 to 50 nm.

The upper electrode 30 of the ONO capacitor unit 6 is formed on the ONOcapacitor interlayer insulating film 28. The upper electrode 30 of theONO capacitor unit 6 is formed using the second silicon layer 52 (referto FIG. 4A). The upper electrode 30 of the ONO capacitor unit 6 and thesubstructure 16 in the MEMS structure unit 4 are formed simultaneouslyusing the second silicon layer 52. Examples of materials used in theupper electrode 30 of the ONO capacitor unit 6 include Poly-Si andamorphous Si. The thickness of the upper electrode 30 of the ONOcapacitor unit 6 ranges from 0.05 to 100 μm.

The second field interlayer film 22 is formed over the upper electrode30 of the ONO capacitor unit 6. One of the contact holes 24 is formedover the upper electrode 30 of the ONO capacitor unit 6.

A transistor which has elements such as a gate oxide film 32 and thegate electrode 34 is formed on the surface of the substrate 10 in aregion of the CMOS circuit unit 8. The gate electrode 34 of the CMOScircuit unit 8 is formed using the third silicon layer 54 (refer to FIG.4C). The superstructure 18 in the MEMS structure unit 4 and the gateelectrode 34 of the CMOS circuit unit 8 are formed simultaneously usingthe third silicon layer 54. Examples of materials used in the gateelectrode 34 of the CMOS circuit unit 8 include Poly-Si and amorphousSi. The thickness of the gate electrode 34 of the CMOS circuit unit 8ranges from 0.05 to 100 μm.

The second field interlayer film 22 is formed over the CMOS circuit unit8. The contact holes 24 are formed on a diffusion layer (source anddrain) 36 of the CMOS circuit unit 8.

Plugs 38 made from a titanium nitride film and a tungsten film areformed inside the contact holes 24 formed in the regions 4, 6, and 8.

A first metal wiring layer 40 connected to the plugs 38 is formed on thesurface of the second field interlayer film 22. Examples of materialsused in the first metal wiring layer 40 are Al, Cu, Ti, TiN, and W. Thethickness of the first metal wiring layer 40 ranges from 0.1 to 3 μm.

A second metal wiring layer 44 are formed on first metal wiring layer40, being coupled with the first metal wiring layer 40 through via holes42. Examples of materials used in the second metal wiring layer 44include Al, Cu, Ti, TiN, and V. The thickness of the second metal wiringlayer 44 ranges from 0.1 to 3 μm. The first metal wiring layer 40 andthe second metal wiring layer 44 are insulated from each other with awiring layer interlaminate film 46 made of silicon oxides. The wiringlayer interlaminate film 46 is, for instance, a CVD oxide film, and thethickness thereof ranges from 0.2 to 1 μm. Chemical mechanical polishing(CMP) is used as necessary during the manufacturing of a semiconductordevice in this embodiment. Therefore, the first metal wiring layer 40and the second metal wiring layer 44 are formed to be approximatelyflat.

A passivation film 48 is formed on the surface of the second metalwiring layer 44. Examples of the passivation film 48 include a CVD oxidefilm, a CVD-SiN film, and a polyimide film. The thicknesses of thepassivation film 48 are 0.1-2 μm, 0.15 μm, and 0.5-20 μm for an oxidefilm, a nitride film, and polyimide film respectively.

An opening 20 in the MEMS structure unit 4 approximately corresponds toa region that includes a movable portion of the superstructure 18 and apart of the substructure 16, and is opened in a way to ensure theprescribed gap between the substructure 16 and the superstructure 18.

According to this embodiment, a MEMS structure, a CMOS circuit, and anONO capacitor are packaged into a single chip. This not only simplifiesthe process and reduces the cost, but also simplifies the system andmakes the system effective against noise.

Examples of applications of the MEMS structure unit 4 include a switch,an acceleration sensor, and an actuator. Examples of applications of theCMOS circuit unit 8 include a temperature sensor for temperaturecompensation, an analog-digital conversion circuit, a logic circuit, aclock, and an analog-digital combined circuit such as power controlcircuit.

A manufacturing method of a MEMS resonator according to one embodimentto which one aspect of the invention is applied will now be describedwith references to the accompanying drawings.

FIGS. 3A to 5B are drawings for describing the manufacturing method ofthe MEMS resonator according to one embodiment to which one aspect ofthe invention is applied. As shown in FIG. 3A, the first silicon layer26 is first formed according to this manufacturing method of the MEMSresonator. Specifically, after forming the device isolation oxide film12 such as Locos or trench film on the substrate 10, a first siliconnitride film 14 is formed, so as to serve as an anchor during a releaseetch process. The first silicon nitride film 14 is the base nitride film14 (refer to FIG. 2). Thereafter, the first silicon layer 26 is formedon the first silicon nitride film 14. Examples of materials used in thefirst silicon layer 26 include Poly-Si and amorphous Si. The thicknessof the first silicon layer 26 ranges from 0.05 to 100 μm. The firstsilicon layer 26 is the lower electrode 26 of the ONO capacitor unit 6(refer to FIG. 2). The lower electrode 26 of the ONO capacitor unit 6 isformed by using the first silicon layer 26.

Subsequently, the lower interlayer insulating film 28A is formed, asshown in FIG. 3B, by oxidizing the surface of the lower electrode 26.Here, the lower interlayer insulating film 28A is included in the ONOcapacitor interlayer insulating film 28 of the ONO capacitor unit 6(refer to FIG. 2).

Thereafter, as shown in FIG. 3C, a second silicon nitride film 28B isformed. Specifically, it is formed on the lower interlayer insulatingfilm 28A and on part of the base nitride film 14. The second siliconenitride film 28B becomes the interlayer insulating film 28B. Theintermediate interlayer insulating film 28B is one of the layers thatconstitute the ONO capacitor interlayer insulating film 28.

Subsequently, the upper interlayer insulating film 28C is formed asshown in FIG. 3C. Specifically, it is formed by oxidizing the surface ofthe intermediate interlayer insulating film 28B. The upper interlayerinsulating film 28C is one of the layers that constitute the ONOcapacitor interlayer insulating film 28.

Thereafter the second silicon layer 52 is formed as shown in FIG. 4A.Specifically, it is formed on the base nitride film 14 and on the upperinterlayer insulating film 28C. Examples of materials used in the secondsilicon layer 52 include Poly-Si and amorphous Si. The thickness of thesecond silicon layer 52 ranges from 0.05 to 100 μm. The second siliconlayer 52 may undergo doping. Examples of doping include ion implantationand thermal diffusion. The second silicon layer 52 becomes thesubstructure 16 in the MEMS structure unit 4 (refer to FIG. 2), as wellas the upper electrode 30 of the ONO capacitor unit 6. The substructure16 in the MEMS structure unit 4 and the upper electrode 30 of the ONOcapacitor unit 6 are formed simultaneously by using the second siliconlayer 52.

According to this embodiment, sharing the layers prevents the number ofprocesses to increase, thereby enabling the simultaneous formation.

Subsequently, the gate oxide film 32 is formed as shown in FIG. 4B.Specifically, the oxidized films formed up to this point are strippedand newly oxidized again. The surface of the second silicon layer 52 isoxidized concurrently with the formation of the gate oxide film 32.Oxidizing the surface of the second silicon layer 52 results in theoxidation of the substructure 16 in the MEMS structure unit 4 and theupper electrode 30 of the ONO capacitor unit 6. The oxidation of thesurface of the substructure 16 in the MEMS structure unit 4 creates thethickness of the gap included in the MEMS structure unit 4. Theoxidation process may be carried out for a plurality of times asnecessary, in order to prepare gate oxide films for different uses suchas one for a low voltage and another for a high voltage. In this case, asecond gate oxidation of the CMOS circuit unit 8 and a subsequentoxidation of the CMOS circuit unit 8 after the second one have a dualpurpose to oxidize the gap of the MEMS structure unit 4. The process forforming the tunnel oxide films such as EEPROM tunnel oxides may also becarried out at the same time. Not only the aforementioned processes forsilicon film deposition but also lithography processes are also carriedout concurrently.

According, to this embodiment, sharing the layers prevents the number ofprocesses to increase, thereby enabling the simultaneous formation.

Thereafter, the third silicon layer 54 is formed as shown in FIG. 4C.Specifically, it is formed on the gate oxide film 32 of the CMOS circuitunit 8 (refer to FIG. 2), the upper electrode 30 of the ONO capacitorunit 6, and the substructure 16 in the MEMS structure unit 4. Examplesof materials used in the third silicon layer 54 include Poly-Si andamorphous Si. The thickness of the third silicon layer 54 ranges from0.05 to 100 μm. The third silicon layer 54 becomes superstructure 18 inthe MEMS structure unit 4, and the grate electrode 34 of the CMOScircuit unit 8. The substructure 18 and the upper electrode 34 areformed simultaneously by using the third silicon layer 54.

According to this embodiment, sharing the layers prevents the number ofprocesses to increase, thereby enabling the simultaneous formation.

Subsequently, a self-aligned silicide (salicide) region 56 is formed asshown in FIG. 4D. Specifically, the oxide film is removed selectively inregions for salicidation (portions for interconnection). Ti is thendeposited on the entire surface so as to undergo heat treatment. As aresult, the portions where the oxide film is removed become silicide bya salicidation process. Alternatively, usage of silicides that canwithstand release etching may allow salicidation of the entire substrateafter depositing the third silicon layer 54, Ti regions that did notbecome silicide by a salicidation process are removed with RCA cleaning.Examples of materials used in the salicide region 56 are Ti, W, Mo, Co,Ni, Ta, Pt, and Pd. The thickness of the salicide region 56 ranges from0.01 to 1 μm.

As described, in the method for manufacturing a MEMS resonator accordingto this embodiment, resistance of silicon layers may be reduced bycarrying out impurity implantation (or thermal diffusion), or bysilicidation. However, the silicidation is optional in the MEMSstructure unit 4. Silicidation is carried out, for instance, if thematerial dissolves in the release process.

Thereafter, the second field interlayer film 22 is formed as shown inFIG. 5A. Specifically, it is formed over the substructure 16 in the MEMSstructure unit 4, the upper electrode 30 of the ONO capacitor unit 6,and the CMOS circuit unit 8. Materials used for the thin film depositionand fabrication include low temperature oxide (LTO), high temperatureoxide (HTO), phospho silicate glass (PSG), boruphosphosilieate glass(BPSG), and spin-on-glass (SOG). Therefore, the second field interlayerfilm 22 is formed to be approximately flat.

As shown in FIG. 5B, the first metal wiring layer 40, the wiring layerinterlaminate film 46, the second metal wiring layer 44, and thepassivation film 48 are formed. First, the contact holes 24 are formedover the substructure 16 in the MEMS structure unit 4, the upperelectrode 30 of the ONO capacitor unit 6, and on the diffusion layer(source and drain) 36 of the CMOS circuit unit 8. The plugs 38 areformed inside the contact holes 24, touching the surface of the salicideregions. The first metal wiring layer 40 coupled with the plugs 38 isformed on the surface of the second field interlayer film 22. The secondmetal wiring layer 44 coupled with the first metal wiring layer 40through via holes 42 is formed on the first metal wiring layer 40. Thefirst metal wiring layer 40 and the second metal wiring layer 44 areformed so as to be insulated from each other with the wiring layerinterlaminate film 46. Chemical mechanical polishing (CMP) is used asnecessary during the manufacturing of a semiconductor device in thisembodiment. Therefore, the first metal wiring layer 40 and the secondmetal wiring layer 44 are formed to be approximately flat. A pluralityof wiring layers may be formed. The passivation film 48 is formed on thesurface of the second metal wiring layer 44.

Subsequently, as shown in FIG. 2, release etching is carried out. Priorto release etching, regions except for the MEMS structure are protectedby etching-resistant organic films such as resist and polyimide films.

According to this embodiment, the MEMS structure unit 4, the ONOcapacitor unit 6, and the CMOS circuit unit 8 are formed simultaneouslyin the process in which the MEMS structure are formed on a siliconsubstrate surface together with semiconductor devices such astransistors. Here, the MEMS structure unit 4, the gate electrode 34 ofthe CMOS circuit unit 8, the lower electrodes 26 and 30 in the ONOcapacitor unit 6 are all composed with silicon deposited layers. Byconcurrently carrying out the process of forming the electrodes orinterlayer insulating films for the MEMS structure unit 4, the ONOcapacitor unit 6, and the CMOS circuit unit 8, a workflow for effectiveproduction is set up without significantly increasing the number ofprocesses. Therefore, these three devices are produced on a single chipwithout causing problems in any of them, Mounting the ONO capacitor unit6 on the chip that includes the MEMS structure unit 4 and the CMOScircuit unit 8 broadens the designing variations of the CMOS circuitunit 8. The CMOS circuit unit 8 may serve as devices such as a detector,an amplifier, an operator, and an AD converter, thereby enhancing theconvenience of products.

According to this embodiment, a MEMS structure, a CMOS circuit, and anONO capacitor are packaged into a single chip. This not only simplifiesthe process and reduces the cost, but also simplifies the system andmakes the system effective against noise.

This embodiment can be applied to products in which a MEMS structureunit and semiconductor devices such as CMOS and ONO capacitor arepackaged in a single chip, the MEMS structure unit being made of siliconmaterials. The fields of application of the MEMS structure units includesensors, radio frequency system, switches, and imaging.

The entire disclosure of Japanese Patent Application No. 2006-338042,filed Dec. 15, 2006 is expressly incorporated by reference herein.

1. A method for manufacturing a microeletromechanical system resonatorhaving a semiconductor device and a microelectromechanical systemstructure unit formed on a substrate, the method comprising: forming alower electrode of an oxide-nitride-oxide capacitor unit included in thesemiconductor device using a first silicon layer; forming, using asecond silicon layer, a substructure of the microelectromechanicalsystem structure unit and an upper electrode of the oxide-nitride-oxidecapacitor unit included in the semiconductor device; and forming, usinga third silicon layer, a superstructure of the microelectromechanicalsystem structure unit and a gate electrode of a complementary metaloxide semiconductor circuit unit included in the semiconductor device.2. A microelectromechanical system resonator comprising: a semiconductordevice formed on a substrate, the semiconductor device including anoxide-nitride-oxide capacitor unit and a complementary metal oxidesemiconductor circuit unit; and a microelectromechanical systemstructure unit formed on the substrate.
 3. A microelectromechanicalsystem resonator according to claim 2, comprising: a first silicon layerused for forming a lower electrode included in the oxide-nitride-oxidecapacitor unit; a second silicon layer used for forming a substructureincluded in the microelectromechanical system structure unit and anupper electrode included the oxide-nitride-oxide capacitor unit; and athird silicon layer used for forming a superstructure included in themicroelectromechanical system structure unit and a gate electrodeincluded in the complementary metal oxide semiconductor circuit unit.